The increasing lifetime of telecommunication satellites and the growing requirements associated with the various missions entail the development of new generations of satellites, an objective of which is to improve the flexibility of missions. Such is the case notably for telecommunications antennas and their associated mechanisms, for which one seeks for example to be able to choose between several zones of coverage and several frequency bands, and thus afford the possibility of modifying the satellite's missions while in orbit.
A telecommunications satellite comprises at least one antenna allowing the emission and the reception of electromagnetic waves. Each antenna comprises at least one reflector whose shape and orientation determine the terrestrial zone covered by the antenna. With the aim of covering several distinct terrestrial zones or a more extensive terrestrial zone than that which can be covered by a single antenna, it is envisaged to implement an antenna reflector whose reflecting surface is deformable.
Various devices allowing the deformation of the reflecting surface of an antenna are envisaged. In a known implementation of an in-service reconfigurable antenna reflector, a deformable reflecting membrane is positioned on a rigid antenna structure, by means of several linear actuators positioned transversely between the rigid structure and the reflecting membrane, and distributed in a substantially uniform manner over the surface of the membrane. Flexibility of coverage is obtained by elastic deformation of the reflecting membrane during a reconfiguration step achievable in orbit.
In this implementation, the linear actuators, fixed on the rigid structure, are connected to the reflecting membrane at various contact points. A translational motion generated by the linear actuator, for example by means of a ram, is transmitted to the reflecting membrane so as to deform its surface and thus reconfigure the zone of coverage of the antenna.
With the aim of ensuring sufficient holding of the membrane to make it possible to withstand high mechanical stresses, notably the vibratory stresses encountered during a launch phase using a launcher spacecraft, it is envisaged to fix the membrane on the rigid structure at the periphery of its surface; holding the membrane on the structure at the periphery does not allow control of the edges of the membrane.
A first difficulty in this implementation pertains to the mechanical stresses undergone by the membrane at these various points of contact with the linear actuators. Indeed, the linear actuators, which do not allow motion of the membrane in a plane tangential to its surface at their contact point, generate a local mechanical stress on the membrane. This local mechanical stress might not be withstood by the membrane and may engender radial loads on the actuators, and may be particularly penalizing in certain situations, such as for example during a satellite launch phase or during large thermal variations in use in orbit.
A second difficulty encountered in this implementation pertains to the global isostatic holding of the membrane with respect to the rigid structure in order to avoid deformation stresses due to hyperstaticity.
The choice of the materials for the reflecting membrane is in practice limited to a few materials able to withstand all these mechanical stresses. Other materials, which are more attractive in terms of reflectivity performance, mass or cost, are discarded because of their fragility.